Although lysophosphatidic acid (LPA) has been known be vasoactive for over 30 years, it is only recently that this compound has been implicated in a wide variety of cell biology. LPA is a prominent component of serum (it is released from activated platelets), where it is mitogenic and exerts powerful effects on cell morphology. In addition, LPA is a calcium mobilizing agonist in many cell types and effects chemotaxis in some cell types. A structurally-related lipid, sphingosine-1-phosphate (S1P) mimics some LPA effects, and thus provides a lead for structure-activity relationship (SAR) studies. Although LPA/S1P are implicated in an intriguing number of cellular events that are reminiscent of G-protein coupled receptor (GCR) activation, work with these lipid mediators is hampered by their poor solubility and metabolic lability, and by the absence of direct evidence that their actions are receptor mediated. With this proposal, two independent investigators with backgrounds in synthetic medicinal chemistry and the molecular biology of G-protein coupled receptors describe a focussed research plan designed to take the biology these important autacoids to a molecular level. We hypothesize that LPA and related compounds, including sphingosine-1-phosphate, can signal cells through a sub-family of G-protein coupled receptors. With interdependent programs in synthetic chemistry and molecular biology, we will develop agonists and antagonists of LPA/S1P that are stable metabolically and exhibit receptor subtype selectivity. Furthermore, we will define the action of these compounds at cloned receptors and will use the recombinant receptors and synthetic compounds to define the LPA-S1P binding pocket. Minimally, our research program will result in the identification and characterization of a stable mimetic and a LPA receptor clone and thus will provide compelling evidence for a physiologic role for these interesting lipid mediators and tools for their further study. Maximally, we will identify and characterize a series of compounds, including antagonists, that interact selectively with a sub-family of LPA receptors. The existence of well-defined reagents, particularly antagonists, for study of signalling by LPA and related compounds will not only enhance understanding of their biology, but may enable ultimately therapeutic modulation of lipid signalling pathway.